The present invention relates to a series of new pyrazole derivatives having valuable herbicidal activity and provides methods and compositions using these compounds, as well as processes for preparing them.
The purpose of herbicides in agriculture and horticulture is to kill unwanted plants (weeds), whilst leaving untouched plants which are wanted (crops). A herbicide is of restricted practical use if it is lethal to all plants. Accordingly, for maximum practical effect, it is desirable to target not only specific weeds, but also the desired crop, to ensure that the herbicide is lethal to the weeds and inactive against the crops. We have now discovered a series of pyrazole derivatives which have this effect.
A number of pyrazole derivatives have previously been described and said to have herbicidal activity. For example, UK Patent Specification No. 1 488 285 and U.S. Pat. No. 4,008,249 disclose compounds of this general type which are said to be useful as herbicides, whilst European Patent Specification No. 14 810 discloses such compounds for the protection of plants from "pests", primarily insects. However, the closest prior art to the present invention is believed to be European Patent Specification No. 7 990 (equivalent to U.S. Pat. Nos. 4,316,040 and 4,298,749), which discloses a wide class of compounds (embracing some of those of the present invention) which are said to have herbicidal activity.
In accordance with the present invention, we have now discovered that a limited class of pyrazole compounds has excellent herbicidal activity against a wide range of weeds (better than that of the prior art) whilst exhibiting no harmful effects on crop plants, notably rice.